An instance of WCheckBox corresponds to an HTML <input type="checkbox"> element.
Next to being checked or unchecked, a checkbox can be configured to allow a third state, Wt::PartiallyChecked, which can be used to indicate that it isn't entirely checked, e.g. if only some of the files in a folder are selected, then the checkbox for that folder would be partially checked. In the example below, the third checkbox demonstrates this tristate behaviour.
By default, check boxes will appear on the same line.
Since by default, check boxes are inline, you will need to use setInline(false) to let them stack vertically.